Belgian teenager Adnan Januzaj has been added to the first-team squad as they prepare to face Chelsea on Sunday and Giggs believes the young players must make a big impact if they are to remain at Old Trafford for the long-term.
"I have seen so many young players over the years have a chance and not really take it," he said.
"Others think 'this is my chance I am going to make sure the manager takes notice' and they perform like they have been doing in the youth team or the reserves.
"Nick Powell did it earlier this season. He came on against Wigan and scored. That is what young players have to do."